1. Field of the Invention
This invention relates to a cemented optic lens having a plurality of optical elements cemented together and a process for producing the same.
2. Description of the Related Art
While the desired performance of the ordinary lens for photography can usually be realized by employing several component lenses to constitute the ordinary lens, it is not rare for the video taking-lens to necessitate more than ten component lenses. And, it is common in many cases that, for the purpose of correcting chromatic aberrations, etc., among these component lenses there are included two or three cemented lenses each consisting of positive and negative lens elements. FIG. 3 shows an example of the conventional taking-lens of the zoom type, wherein three component lenses labeled x, y and z are the cemented lenses.
Very briefly explaining, the process for producing a component lens comprises the steps of: cutting raw optical glass to the equivalent size, pressing, roughing (grinding), smoothing and polishing. Not only the component lens to be used as a singlet but also the component lenses to be used to constitute a cemented lens have to undergo a likewise process.
This is because even in the case of the cemented lens, its cemented surface must satisfy a predetermined transmission factor and conversely because, if scattering or the like occurs, an opportunity for deteriorating the optical performance would otherwise be involved. Hence, it has been the usual practice that even those surfaces of the lens elements which are to be cemented together are polished.
However, the cemented lens will be essentially sufficient if a prescribed function is satisfied as one component lens after the lens elements are cemented together. Hence, it is also possible to take a conception that there is no need to polish the lens surfaces which are to be cemented, since they are merely one element of its internal structures. This also can be guessed from the example of employment of a cemented lens in which a lens surface of a molded lens and a lens surface of a polished lens are cemented together in a photographic lens disclosed in Japanese Laid-Open Utility Model Application No. Sho 59-184101.
For example, even in the lens of popular optical glass, say, BK7, and of a small diameter of 2 to 3 cm, its polishing takes as long a time as 3 minutes. Taking into consideration the additional work of setting and removing the lens onto and from the tool, the total required time is not negligibly short. If the necessity of this step is obviated, it can be expected to achieve a remarkable reduction of the production cost since it considerably reduces the necessary number of steps in manufacturing lenses in the factory.